1. Field of the Invention
The invention relates to an actuating device, especially a hydraulic or pneumatic actuator, for transmissions of vehicles, particularly motor vehicles. The actuating device comprises a housing in which two pistons are arranged. A coupling part that is connectable to a shifting part, preferably a shift fork, is movable by means of the two pistons. The coupling part, at least at its surface, is made of a wear-resistant material, preferably steel.
2. Description of the Related Art
Known actuating devices of this kind are provided for different applications in the field of vehicle transmissions. In this connection, shift forks in the transmissions are actuated directly by a hydraulic or pneumatic actuator. The cylinder housing of these actuators are integrated into the transmission housing and are comprised of aluminum. The shift forks actuating the actuators must transmit great forces in the transmission. For this reason, the contact location relevant for the force transmission or the corresponding part of the actuator are manufactured of a hard, wear-resistant material, preferably steel. Because of leakage requirements, the weight, and the temperature behavior, the piston is comprised of the same material as the actuator or cylinder housing, i.e., is comprised of aluminum. For reasons of force transmission of the piston onto the shift fork, the piston should be made of steel. In a known actuator, the cylinder housing is integrated into the transmission housing. The piston is comprised of several parts. The parts of the piston provided with the running surface and the sealing surface of the piston are comprised of aluminum; the contact location relative to the shift fork is comprised of a steel part. A disadvantage is that the pistons are comprised of several parts wherein the running surfaces of the piston are distributed over several components. When mounting the piston, a contact member comprised of steel is inserted. Subsequently, the other piston parts comprised of aluminum are connected to one another, for example, by pressing, screwing or welding. After this connecting step, there is the danger that the running surfaces of the piston are no longer precisely aligned relative to one another; the piston therefore must be after-machined on a machine in order to comply with the predetermined geometric requirements. This is complex and expensive.